1. Field of the Invention
This invention relates to the field of dynamic hydraulic seals, particularly to seals that move into sealing contact due to hydraulic pressure and retract from such contact when pressure is removed.
2. Description of the Prior Art
Many different techniques have been used to produce a dynamic hydraulic seal where reciprocating or rotary motion occurs between parts being sealed. An O-ring is a positive seal that is squeezed at the top and bottom surface of its groove against the mating part. It is capable of sealing very high pressure, which forces the seal against the side of its groove thereby producing a positive seal on three surfaces. O-rings are usually limited to reciprocating parts having relatively short motion, e.g., a valve spool located in a chamber of an hydraulic circuit. A backup ring is often used with an O-ring to prevent its being extruded into the space between the mating parts.
Other dynamic seals include backup rings, lathe-cut O-rings and T-ring seals. A lathe-cut seal is an O-ring having a square cross-section. A T-ring is used in reciprocating dynamic applications to maximize the contact pressure on the sealing surface.
A lip seal is a dynamic seal used principally on rotating shafts to provide a positive seal against relatively low pressure. The lip seal is installed toward the pressure source, which causes deformation of the seal and forces the seal against a contact surface.
In an automatic transmission it is necessary .to carry hydraulic fluid from passages formed in the transmission casing to a rotating component, such as a planetary pinion carrier or a rotating shaft. It is conventional practice to locate an O-ring seal on opposite axial side of the passage by arranging a connection such that the pressure of the hydraulic fluid forces the O-rings against the lateral surfaces of their grooves so that a high quality pressure seal results. This arrangement, however, maintains a frictional drag force on a rotating component because the O-rings require an interference fit between the transmission casing and the rotating component. This continual drag force lowers the overall operating efficiency of the transmission by drawing power from the internal combustion engine to overcome the drag losses.
U.S. Pat. No. 4,718,820 describes an annular grease seal for sealing a rotating shaft in the casing of the fluid pump. A grease fitting permits grease to flow around bearings supporting the shaft and to reposition the grease seals adjacent the bearing to an upright position.